Microfluidic devices allow manipulation of extremely small volumes of liquids, and therefore are particularly useful in small scale sample preparations, chemical synthesis, sample assay, sample screening, and other applications where a micro-scale amount of samples are involved. For many applications, the chemical make up of the resulting material (i.e., sample) needs to be analyzed. Such analysis typically requires at least some degree of sample purification and/or separation. However, due to the small sample size (e.g., nanoliter to microliter) used by these microfluidic devices, conventional separation techniques are not applicable.
Use of packed capillary and open tubular liquid chromatography (PCLC and OTLC, respectively) separation techniques have become increasingly popular due to the demonstrated means of achieving high chromatography efficiency with low operation pressures. Conventional high performance liquid chromatography (i.e., HPLC) typically requires >2000 psi pressure. In contrast, pressure of as low as 5 psi can be used for OTLC and PCLC. Some of the advantages of the OTLC and PCLC techniques include, but are not limited to: (1) an increased efficiency, (2) a lower sample dilution requirement, thereby increasing the sample detection sensitivity, e.g., using a mass spectrometer, (3) a smaller amount of eluent requirement, and (4) the small sample amount requirement. The latter advantage is of particularly importance in a variety of fields, such as proteomics, genomics, forensics, and other areas where a minute quantity of sample is to be separated or purified. Unfortunately, in order to achieve the desired sensitivity and efficiency in OTLC and PCLC, the inner diameter of OTLC and PCLC columns need to be small, generally in the order of 50 μm or less, and preferably about 10 μm or less. The small column diameter size in OTLC and PCLC techniques requires an equally precise sample injection and pumping system. To be effective, OTLC and PCLC techniques require a sample flow rate of 0.01 μL/min or less. Conventional sample pumping system can not adequately meet this stringent requirement. In addition, difficulties with large interconnection dead volume and detection volume between the OTLC or PCLC column and the fluid delivery (i.e., pumping) system have greatly limited the application of OTLC and PCLC techniques.
Therefore, there is a need for OTLC and PCLC devices which comprise a sample injection and fluid pumping system that can achieve a sample flow rate of 0.01 μL/min or less. There is also a need for OTLC and PCLC devices which have small or no dead volume between the OTLC or PCLC column and the fluid delivery system.